http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Symmetry Effects on Magnetocrystalline Anisotropy of hcp and fcc Cobalt: a First-principles Study
Thi H. Ho,Sonny H. Rhim,S. C. Hong 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Density-functional theory calculations are performed to investigate symmetry effects on magnetocrystalline anisotropy (MCA) of Co. Both bulk and films in the hcp and fcc phases are considered. Within the framework of second-order perturbation theory<sup>[1]</sup>, MCA energy can be decomposed into spin channels, i.e., the spin-conserved ↑↑ and ↓↓, and the spin-flip ↑↓ and ↓↑ terms. Here, the first spin (↑ or ↓) symbol represents an occupied state, while the second spin (↑ or ↓) one does an unoccupied state. For example, ↑↓ represents the coupling between an occupied ↑ state and an unoccupied ↓ state. The spin-channel decomposed MCAs of hcp and fcc Co in bulk are presented in Fig. 1. Generally, each spin channel contribution behaves in a quite similar way for both hcp and fcc Co. However, the net MCAs are quite different, 15.61 µeV/atom of hcp Co and 0.53 µeV/atom of fcc Co, whose reason should be revealed. In both hcp and fcc Co, the majority spin(↑) bands are almost completely filled so that the negligible unoccupied ↑ states cannot play a dominant role in determining a MCA energy. As a result, the spin channels of ↑↑ and ↓↑ contribute much smaller than those of ↓↓ and ↑↓, as shown in Fig. 1. The big difference between the MCAs of hcp and fcc Co comes mostly from the positive spin-flip ↑↓ and the negative spin-conserved ↓↓ terms. The negative spin-conserved ↓↓ term of hcp Co is much smaller by 13.17 µeV/atom in absolute value than that of fcc Co, while the positive spin-flip ↑↓ term of hcp Co has higher MCA by 2.0 µeV/atom than that of fcc Co, which results in the much stronger MCA of hcp Co than fcc Co. In thin films, the surface effects are found to enhance MCA energies of both hcp and fcc Co. For the 9-ML films, the MCA energies of 253.04 and 207.64 µeV are obtained for hcp and fcc Co, respectively. Interestingly, the MCA energy of the fcc Co film is in the same order of magnitude as that of the hcp Co film. The reason is due to the dominant MCA contribution of the surface layers. The MCA values of surface layers are 171.8 and 188.7 µeV/atom for the hcp and fcc Co, respectively.
Spin Hall Conductivities of W-N Alloys
Quynh Anh T. Nguyen,D. D. Cuong,S. C. Hong,Sonny H. Rhim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Motivated by recent reports on high spin Hall angle in W alloys [1-3], spin Hall conductivities (SHC) of W-N alloys are investigated theoretically using ab initio density functional calculations. Without N, SHC of α-W and β-W are -744 and 818 ℏ/S/cm, respectively. Among various combinations, we focus on W<sub>2</sub>N and WN. In particular, SHC of W<sub>2</sub>N is enhanced 18.7 % over β-W. High SHC of W<sub>2</sub>N is elucidated by large Berry curvature from 2/3rx. On the other hand, in WN case, three structures, NaCl-type, hexagonal and NbO-type, are considered. SHC of NaCl- and hexagonal types are -619 and –696 ℏ/S/cm, respectively, while NbO-type exhibits relatively low SHC of –194 ℏ/S/cm. However, considering energetics, W<sub>2</sub>N is more promising than WN, whose thermodynamic average is around –194 ℏ/S/cm.
Giant Spin-orbit Torques Induced by Orbital Hall Effect
Soogil Lee,Junho Kang,Taekhyeon Lee,Jung-Mok Kim,Dohyoung Kim,Heechan Jang,Eun Kang Park,Dongwook Go,Nyun Jong Lee,Yoshinori Kotani,Yoichi Shiota,Teruo Ono,S. Sonny Rhim,Kyung-Jin Lee,Hyun-Woo Lee,Kab 한국자기학회 2019 한국자기학회 학술연구발표회 논문개요집 Vol.29 No.2